The invention relates to data storage media and, more particularly, to techniques for monitoring servo tracks in magnetic media.
Magnetic media are used for storage and retrieval of data, and come in many forms, such as magnetic tape and magnetic disks. A write/read head assembly, which includes one or more write/read transducer heads, reads data from and writes data to the magnetic medium. The data stored on the medium are usually organized into xe2x80x9cdata tracks,xe2x80x9d and the transducer heads write data to and read data from the data tracks.
Data tracks on magnetic tape are generally parallel to each other, and often are oriented longitudinally on the tape. The head assembly is usually oriented transverse to the path of the magnetic tape so that the transducer heads move laterally across the width of the tape to access the tracks. On a magnetic disk, the data tracks are generally arranged as concentric circles or a spiral pattern on the disk, and the head assembly typically moves along a radius of the disk to access the tracks.
For efficient reading and writing, a transducer head must be accurately positioned to read from or write to a particular data track. A servo control loop typically is provided to control the positioning of the head relative to the data tracks. The medium often includes specialized tracks, called xe2x80x9cservo tracks,xe2x80x9d to serve as references or landmarks for the servo. Data tracks can be located on the magnetic medium according to the data tracks"" displacement from one or more servo tracks. Servo tracks may include magnetic markers, in which case the surface of the medium is homogeneous but the servo track can be detected magnetically. Another type of servo track is a physical mark on the medium, such as a groove. With this type of servo track, the medium surface is not homogeneous but is physically altered at the site of the servo track. Servo tracks of the latter type can be detected optically.
The invention is directed to diffraction-based monitoring of a magnetic recording medium to verify the formation of servo tracks. A diffraction-based monitoring technique can be used, for example, as quality assurance measure in manufacture of magnetic media with servo tracking.
A xe2x80x9cservowriterxe2x80x9d is a device that is configured to form physical servo tracks on a magnetic medium. One way to make a physical servo track on a magnetic medium is to ablate the medium with a laser. A laser can mark very fine servo tracks, a few microns in width, in the medium and can do so with good accuracy and precision. It is important, however, to be able to inspect the magnetic medium after marking to evaluate whether the servo tracks formed by the laser meet applicable quality standards. Quality standards may govern, for example, the spacing between servo tracks or the depth or shape of the tracks. In addition, it may be useful to monitor the process of placing servo tracks by laser while servo tracks are being formed so that improperly formed servo tracks may be detected and so that corrections may be made during manufacture of the medium.
The invention provides high-speed techniques for monitoring servo tracks that physically alter the recording medium. If the tracks are periodic, then directing a beam of coherent light on the medium will generate a reflected diffraction pattern. By monitoring the diffraction pattern created by the servo tracks, the characteristics, and therefore the quality, of the servo tracks can be evaluated. In one embodiment, the invention presents a system comprising a light source such as a laser that directs light upon two or more physical marks on a surface of a magnetic recording medium. The physical marks may be servo tracks, and light striking the surface of the medium produces a diffraction pattern. A light detector such as a photodiode detects at least a portion of the diffraction pattern. The detector may generate a signal as a function of the part of the diffraction pattern detected by the detector. The apparatus may be configured to monitor one or more diffractive orders of the diffraction pattern.
In another embodiment, the invention presents a method, comprising illuminating a surface of a magnetic recording medium. The medium has two or more physical marks such as servo tracks, and illuminating the medium generates a diffraction pattern. The method further includes detecting at least part of the diffraction pattern. In addition, a signal may be generated as a function of the detected diffraction pattern.
In a further embodiment, the invention presents a method comprising forming servo tracks on magnetic media, illuminating a region of the magnetic media to generate a diffraction pattern, detecting at least part of the diffraction pattern, generating a signal as a function of the detected diffraction pattern and forming subsequent servo tracks on the magnetic media as a function of the signal. This method allows the diffraction pattern to operate as part of a feedback system in the process of marking servo tracks.
In an additional embodiment, the invention presents a system that implements a feedback system. The apparatus includes a marking device configured to form servo tracks on magnetic media, a light source configured to direct light upon the media and generate a diffraction pattern and a light detector configured to detect at least part of the diffraction pattern, and to generate a signal as a function of the detected diffraction pattern. The marking device is configured to form subsequent servo tracks on the magnetic media as a function of the signal.
In another embodiment, the invention presents a method, comprising illuminating a surface of a magnetic recording medium to generate a diffraction pattern, detecting at least part of the diffraction pattern and generating a signal as a function of the detected diffraction pattern. The diffraction pattern can result from servo tracks on the medium, and the signal can be a function of various characteristics of the servo tracks.
The details of one or more embodiments of the present invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the present invention will be apparent from the description and drawings, and from the claims.